Prop Testing - NTM Prop Drive 35-36A 1800Kv / 875w

Thank you ttprigg.

First let me say that I am no expert by any means. What knowledge I do have has been learned over the past several months by doing a lot of reading, Google searches, forum posting and of course the FliteTest crew and community. I just got back into this hobby about six months ago after about 15 years. Back then it was all gas and nitro so "electric" is kind of new to me.

That being said I will try to answer your question. I also welcome feedback and input from other readers as well. After all this is a learning process and having an open discussion is the best way to learn and share ideas.

In your post you mention that you have always assumed that the max-amp rating given by the manufacturer was something that could not be exceeded without potential consequences. You also ask how it would be possible, given my results, to achieve the exact manufacturer rating of 700W @ 12v (3S) or 875W @ 15v (4S).

From what I have learned the manufacturer rating of the motor is a number they give you to let you know what they consider to be the safe limit and optimal power level for the motor. It also lets you know that if you decide to take the chance and run it at higher power levels it is at your own risk. In other words, if you run it higher than what they recommend and the motor burst into flames it is now your problem, not theirs.

The ability of the motor to safely run at higher power levels than the manufacturer rating is dependent on many factors. Some of which are air flow (is the motor and ESC getting good ventilation), ambient temperature (is it a cool winter day, or is it blistering hot like it gets where I live, South Florida), the battery discharge rating or "C" rating (can the battery deliver the amount of power the motor is asking for), last but not least the quality of the parts (motor, ESC and battery). All these factor will determine how "hot" your electronics will get and heat is what can kill them.

As you can see the most important factor here is heat. Heat is your enemy. For example even if your setup gives you numbers below the manufacturer rating if you do not have enough ventilation flowing over the ESC and the motor you still run the risk that they will burst into flames. On the other hand if your setup is producing numbers that are higher than the manufacturer rating but you provide plenty of ventilation and it is also a cool winters day then you should not have a problem. Unless of course you run numbers so high that even good ventilation is not enough to keep the motor and/or the ESC from overheating.

As far as the second part of your question, "how do you get to the Max Power", keep in mind that the power output is constantly changing and even when you do get the exact "max power output" it does not stay constant for very long. What I mean by this is that when you have a battery that is fully charged the second you open up the throttle and spin up the motor the voltage of your battery starts to decrease. As the voltage of your battery decreases the power output of the motor also decreases. Another factor to think about is prop resistance. When you are holding onto your plane on the ground and you spin up the motor it has to work a little harder to spin the prop than it would if the plane was up the the air in flight. So the numbers you get on the ground while holding the plane are usually a bit higher than when the plane is flying in the air. When on the ground while holding the plane you get 70 amps at 720 watts then you can assume that in flight those numbers will drop to around 65 amps at 700 watts. Still keep in mind that those numbers will never be constant for long because the voltage of your battery is always changing.

To sum this all up I think the best way to think about the "manufacturer rating" is that they are giving you a ball park number that you should try to stay as close too as possible. Whether you decide to exceed those numbers or not you still need to make sure that the electronics do not overheat because in the end it is not amps or watts that kill your electronics, it is heat produced by the electricity that will damage them. More amp/watts means more heat = taking off as a plane and landing as a ball of flames... lol

I hope that my long winded reply can shed a little clarity on this subject for you and as I mentioned at the start of this I welcome any input from other readers as well.

Rock ON!
fretsman
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Thank you Flat4. Yes I remember you from the forum on my post about this motor. Looking forward to comparing notes with you. Pull that thing out of the box soon! :)

Rock ON!
fretsman

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Thank you :)
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Thank you InvertedG.

To answer your question.... I only ran the props for about 15 seconds at full throttle then backed of slowly so even when I recorded very high numbers neither the motor nor the ESC got very hot at all.

That being said I can tell you from actual flight testing what combination I have found works best for me. I put this motor on my new scratch built FT Viggen and I have been flying it with two different setups. On both setups the motor and the ESC only get warm to the touch.Using the 4 cell setup the motor does get a bit warmer but it is still what I would consider safe. Setup details are below...

3 cell setup = Turnigy nano-tech 2700mah 3S 65~130C with an APC 8 x 4 prop

4 cell setup = Turnigy nano-tech 2200mah 4S 45~90C with an APC 7 x 6 prop

Since the 4 cell setup does result in the motor getting a bit warmer I would consider running it using an APC 7 x 5 prop instead of the 7 x 6. I did not test with a 7 x 5 prop yet but from Team Monkeys post below it looks like that just may be the sweet spot for a 4 cell and this motor. I will try one next time I fly and post results here.

Rock ON!
fretsman
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Thank you Team Monkey!

I remember you posted on my forum post about this motor. I also saw your video of the delta wing. Awesome... Great plane and nice build...

Rock ON!
fretsman
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